The present invention relates to a toner for use in an image forming method, such as electrophotography, electrostatic recording and toner jetting, and an image forming method using such a toner.
Hitherto, various electrophotographic image forming methods have been proposed, e.g., in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. Generally, in these methods, an electrical latent image is formed on a photosensitive member using a photoconductor material by various means and then developed with a toner to form a toner image. The toner image is transferred onto a transfer material such as paper, as desired, directly or indirectly, and fixed onto the transfer material, e.g., by heating, pressing or heating and pressing or with solvent vapor. Further, in the case of including such a step of transferring toner image, a step of removing the transfer residual toner onto the photosensitive member is generally included, and the above-mentioned steps are repeated for subsequent image forming cycles.
Particularly, in full-color image formation, electrostatic latent images and generally developed with a magenta toner, a cyan toner, a yellow toner and a black toner to form respective color toner images in superposition to reproduce multicolor images.
Further, in recent years, apparatus utilizing electrophotography have been used not only as copying machines for reproducing originals but also for printers for computers, personal copiers for individual users and facsimile apparatus using plain paper, thus being rapidly developed and various requirements being posed thereon. Also for copying machines, development to a higher functionality is being effected by digital image forming technique. Particularly, extensive development has been made regarding size reduction, higher speed and color image formation by the image forming apparatus, and further higher reliability and resolution are being strongly desired. For example, the required resolution which was at a level of 200-300 dpi (dots per inch) has been enhanced to 400-1200 dpi, and further to a level of 2400 dpi.
In contrast with such demands, it has been a general trend that image forming apparatus are designed to be composed of simpler parts and elements. As a result, further higher functionality is required of a toner, it is a present state that a better image forming apparatus cannot be accomplished without realization of further improved toner performances.
For example, in recent years, as a transfer device for electrostatically transferring a toner image on an (electrostatic latent) image-bearing member or an intermediate transfer member onto a transfer material, a so-called contact or abutting transfer device including a roller-shaped transfer member supplied with a voltage from an external supply and abutted against the image-bearing member or intermediate transfer member via the transfer material is being increasingly used from the viewpoints of size reduction of the enter image forming apparatus and prevention of ozone generation.
For such an abutting transfer device, the sphering of a toner particle shape is effective for providing an improved transferability and enhancing the durability against mechanical stress exerted by the device, but on the other hand, this results in smaller specific surface area and volume of toner particles, so that the dispersibility of a colorant inside the toner particles seriously affects the transferability and matching with the transfer device of the toner particle.
Further, in a conventional electrophotographic image forming apparatus, a corona discharger utilizing corona shower generated by applying a high DC voltage of 6-8 kV to a metal wire has been frequently used as a non-contact charging means for uniformly charging a surface of an image-bearing member such as a photosensitive drum as a member to be charged. Such a non-contact charging means is very effective as a means for uniformly charging the image-bearing member surface to a desired potential but leaves problems regarding size reduction of image forming apparatus, use of lower-voltage power supply, prevention of ozone generation, and longer life of photosensitive drum and charging device. For this reason, in recent years, a so-called contact charging means using a charging member contacting the image-bearing member and supplied with a prescribed voltage to charge the image-bearing member has been widely commercialized.
The charging member or charge-supply member used in such contact charging means may assume various forms inclusive of rollers, blades, brushes and magnetic brushes. Among these, an electroconductive roller-form charging member (hereinafter sometimes referred to as a xe2x80x9ccharging rollerxe2x80x9d) has been preferably used from the viewpoint of charging stability.
The surface charging of a member to be charged by the contact charging means may be effected by (1) direct charge injection from the charging member to the member to be charged, or (2) minute discharge caused between the charging member and the member to be charged. For the former charging mechanism, the image-bearing member as a member to be charged has to be provided with a surface charge injection layer (chargeable layer), and for the latter mechanism, it is necessary to apply a bias voltage in excess of a discharge threshold voltage to the charging member.
In the case where the latter mechanism is used for providing a photosensitive member surface potential Vd (dark-part potential) required in latent image formation in an electrophotographic image forming method according to a DC-charging scheme of using a DC voltage component alone for application to the charging member, it is necessary to apply a DC voltage corresponding to the sum of Vd and Vth to the charging member such as a charging roller.
On the other hand, an AC-charging scheme of applying a bias voltage obtained by superposing an AC voltage component of at least 2xc3x97Vth with a DC voltage corresponding to a desired Vd is also known as disclosed in JP-A 63-149668. This is an excellent charging scheme for obtaining a charged state of the charged member which is less affected by environmental conditions by utilizing a smoothing effect of the AC voltage for charging the charged member to a potential Vd which is a central value of the AC voltage applied to the charged member. This charging scheme has left room for improvement regarding a size reduction of voltage supply and a longer life of photosensitive drum as the charged member.
For the above-mentioned contact charging means, it is necessary to provide an appropriate degree of intimate contact between the charging member and the charged member. Accordingly, the charging roller for example controls its abutting state against the charged member by having a resistance layer imparted with a moderate elasticity on an electro-conductive support, thereby aiming at an improved charge uniformity on the charged member and prevention of charge leakage due to pinholes or damages on the charged member. However, it is difficult to maintain such a good contact state between the charging member and the charged member, thus being liable to result in image defects due to charging failure which has been left as a problem to be solved. For example, if transfer residual toner remaining on the photosensitive drum surface is attached to the charging roller surface, the roller surface resistivity is locally increased to fail in uniform charging of the photosensitive drum surface, thus resulting in image defects, such as image fog, image density irregularity and streak image defects in worse cases.
The above-mentioned problems become pronounced in the case of using a small diameter photosensitive drum for which improvements in cleaning of transfer residual toner and intimate contact between the charging member and the drum as the charged member are difficult, or in the case of using a higher process speed, and have provided technical obstacles against the use of smaller image forming apparatus, and a lower voltage supply, a higher image quality and a higher durability. Moreover, these problems are pronounced in the DC-charging scheme showing less smoothing effect compared with the AC-charging scheme and are liable to be pronounced in a low temperature/low humidity environment.
On the other hand, in a fixing device for fixing a toner image onto a transfer material, there has been generally used a heat fixing means comprising a pair of heating roller as a rotatory heating member and a pressure roller as a rotatory pressing member (which may be inclusively called fixing roller(s)), and the heat fixing means requires an instantaneously generated large quantity of heat and a high pressing force for realizing a high-speed image formation. This is liable to be accompanied with difficulties, such as a larger size fixing device and longer start-up preheating time. In view of these points, a toner used in such an image forming apparatus should desirably show a high sharp-melting characteristic when heated. Such a toner can have not a low-temperature fixability but also a good color mixability in full-color image formation, thus providing a broader color reproducibility range of fixed images.
However, such a toner having a higher affinity with a fixing roller is liable to cause an offset phenomenon, i.e., transfer of the toner onto the fixing roller surface at the time of fixation, which is liable to be caused remarkably at the time of full-color image formation.
In order to obviate the above difficulties, it has been practiced to form a fixing roller surface of a material such as silicone rubber or a fluorine-containing resin showing good releasability with respect to the toner so as to prevent the toner attachment onto the fixing roller surface and, in addition thereto, to apply an offset-prevention liquid for the surface of preventing the offset phenomenon and also the deterioration of the fixing roller surface.
The above method is very effective for preventing the offset phenomenon but is accompanied with difficulties such that (1) the inclusion of a device for applying the offset-preventing liquid results in complication of the fixing device, thus obstructing the designing of a small-size and inexpensive image forming apparatus; (2) the applied offset-preventing liquid sinks in the fixing roller, thus being liable to induce peeling between the respective layers constituting the fixing roller and shorten the life of the fixing roller consequently; (3) the offset-prevention liquid attached to the fixed image provides a sticky touch to the fixed image and results in a lowering in transparency of the fixed image when a transparent film is used as the transfer film for an overhead projector (OHP), thus obstructing the reproduction of a desired roller; and (4) the offset-preventing liquid is liable to soil the interior of the image forming apparatus.
On the other hand, the transfer materials used in such image forming apparatus are also diversified inclusive of, e.g., papers having different basis weights and different starting materials and fillers. Among these transfer materials, some are liable to cause separation of the ingredients. The diversity of transfer materials seriously affects the fixing device, thus obstructing the smaller size and longer life of a fixing device.
Further, in some cases, some soiling substance originated from a transfer material forms a lump together with a toner, which sticks to the fixing roller, thus lowering the performance of the fixing device and impairing the product image quality due to peeling thereof.
More specifically, regenerated paper formed from regenerated pulp obtained from once-used paper after ink removable is being increasingly used from the ecological viewpoint. However, regenerated paper is liable to contain various impurities, of which the control is necessary for use in image forming apparatus as described above as proposed in JP-A 3-28789, JP-A 4-65596, JP-A 4-147152, JP-A 5-100465 and JP-A 6-35221.
Regenerated paper for general office use contains more than 70% of regenerated pulp from used paper of newspaper, and the content thereof is assumed to further increase, thus being liable to result in the above-mentioned difficulties. Further, in the case where the heating roller is equipped with a cleaning member for removing the fixing residual toner from its surface or a separation member for preventing the winding of the transfer material, it has been confirmed that the fixing roller surface is damaged with scars or abrasion or the functions of the cleaning member and the separation member are remarkably lowered due to medium-quality pulp fiber contained in paper dust liberated from regenerated paper from medium quality used-paper, such as that of newspaper or magazines. The above difficulties are liable to be serious in the case of using a fixing device using no or only a small amount of offset-preventing liquid.
As noted above, however, the application of an offset-preventing liquid onto a fixing roller surface of a fixing device is accompanied with several problems in spite of effectiveness thereof.
In view of the requirements of a smaller size and a smaller weight for image forming apparatus and quality of fixed images in recent years, it is preferred to remove even an auxiliary means for applying an offset-preventing liquid.
Under such circumstances, it is essential to develop a toner showing improved performances in heat-pressure fixation; and some proposals have been made for that purpose.
For example, many proposals have been made to add a wax component, such as low-molecular weight polyethylene or polypropylene, in a toner, based on the concept of supplying an offset-preventing liquid from inside the toner at the time of heating. In this case, in order to exhibit a sufficient effect, such a wax component has to be added in a large amount to the toner, and other difficulties, such as filming on the photosensitive member and soiling of the toner-carrying member, such as a particulate carrier or a sleeve, are liable to occur, thus causing image deterioration. On the other hand, in the case of adding a small amount of such a wax component, it becomes necessary to equip a device for supplying some offset-preventing liquid or an auxiliary cleaning member, such as a takeup roll-type cleaning web or cleaning pad. Particularly, in the case of full-color image formation, the problem of inferior transparency or haze of the fixed image of the fixed image on a transparency film as a transfer material has not been solved.
Thus, while the inclusion of a wax component has been proposed in, e.g., JP-B 52-3304, JP-B 52-3305, JP-A 57-52574, JP-A 60-217366, JP-A 60-252360, JP-A 60-252361, JP-A 61-94062, JP-A 61-138259, JP-A 61-273554, JP-A 62-14166, JP-A 1-109359, JP-A 2-79860 and JP-A 3-50559, it has been difficult to achieve the high degree of improvement in performances required of a toner, by such proposal of wax component alone and sufficient matching with image forming apparatus adopting the heat-pressure fixing system has not been realized yet.
On the other hand, the use of various pigments and dyes as colorants is known in order to provide an improved color reproducibility of color toner images.
Particularly, a magenta toner is not only important for reproducing a red color to which human visual sensitivity is higher in combination with a yellow toner but also required to exhibit excellent developing performance in order to reproduce delicate tints of human skin colors. Further, a magenta toner is also required to show a good reproducibility of a secondary color of blue which is frequently used as a business color, in combination with a cyan toner.
Hitherto, for providing a magenta toner, it has been known to use quinacridone colorants, thioindigo colorants, xanthene colorants, monoazo colorants, perylene colorants, and diketopyrrolopyrole colorants, singly or in combination of two or more species.
For example, toners containing 2,9-dimethyl-quinacridone pigment (JP-B 49-46951), thioindigo pigment (JP-A 55-26574), xanthene dye (JP-A 59-57256), monoazo pigment (JP-A 11-272014), diketopyrrolopyrole pigment (JP-A 2-210459) and anthraquinone pigment (JP-B 55-42383), have been proposed respectively.
However, such colorants as mentioned above do not necessarily satisfy all requirements for providing a magenta toner. Particularly, many colorants for a magenta toner have poor dispersibility so that the dispersed particles thereof are liable to scatter incident light to result in lower transparency of fixed image and lower color reproducibility. Further, most of them have left room for improvement regarding toner tints, light-fastness, chargeability and matching with image forming apparatus.
JP-A 1-224777 has proposed the co-use of quinacridone organic pigment and xanthene dye, and JP-A 2-13968 has proposed the co-use of quinacridone and methine colorants, for providing clearer magenta color toners and improved chargeability and light-fastness of toners while preventing dyeing of a fixing roller such as a silicone rubber roller. Further, JP-A 62-291666 (corr. to U.S. Pat. No. 4,777,105) has proposed the use of quinacridone pigment in a mixture crystal state.
Further, JP-A 2000-18114 has proposed a toner using a color-adjusted pigment produced from dimethylquinacridone and a red pigment showing a negative chargeability or weak chargeability.
On the other hand, JP-A 11-52625 has proposed the co-use of a red pigment classified under C.I. Pigment Red 48, and a quinacridone pigment showing a b* value of xe2x88x925 or below according to the L*a*b* colorimetric system in a mixing proportion of 2-30 wt. % with respect to the total pigments so as to provide a good magenta color toner while improving the chargeability and light-fastness of the toner and the thermal resistance of the fixing roller.
However, any of the toners containing the above-mentioned colorants have almost failed to pay consideration to influence of the colorants onto the abutting transfer performance and heat-pressure fixing performance. Particularly, no consideration has been paid to the case of using regenerated paper containing more than 70% of regenerated pulp as a transfer material, the case of color image formation requiring simultaneous fixation of plural toner layers or the case of using a fixing device wherein no or only a small amount of offset-preventing liquid is applied onto a fixing roller.
As described above, no toner can be said to be sufficient after overall consideration in connection with a colorant of system designing including the transfer scheme using the abutment transfer mode and the heat-pressure fixing scheme.
A generic object of the present invention is to provide a toner having solved the above-mentioned problems of the prior art.
A more specific object of the present invention is to provide a magenta toner excellent in color reproducibility, gradation characteristic, light-fastness and chargeability.
Another object of the present invention is to provide a magenta toner capable of forming a high resolution and high-definition fixed image.
Another object of the present invention is to provide a magenta toner capable of forming non-sticky high-quality full-color images at an excellent color reproducibility.
Another object of the present invention is to provide a magenta toner capable of forming a fixed image at an excellent-transparence on a transparency film.
Another object of the present invention is to provide an image forming method using a magenta toner as described above.
A further object of the present invention is to provide an image forming method capable of forming fixed images at a good fixing state on various qualities of transfer materials even by using a heat-pressure fixing means where only a small amount of or no offset-preventing liquid is applied onto a fixing member.
According to the present invention, there is provided a toner, comprising: at least a binder resin, a colorant and a wax component;
wherein the colorant comprises a monoazo pigment composition comprising a monoazo pigment represented by Formula (1) below, a xcex2-naphthol derivative represented by Formula (2) below and an aromatic amine represented by Formula (3) below,
the monoazo pigment composition is contained in a proportion of 1-20 wt. parts per 100 wt. parts of the binder resin, and
the xcex2-naphthol derivative and the aromatic amine are contained in proportions of 500-50,000 ppm and at most 200 ppm, respectively, based on the monoazo pigment composition;
Formula (1): 
wherein R1-R3 independently denote a substituent selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, nitro, anilido and sulfamoyl; R4 denotes a substitutent selected from the group consisting of xe2x80x94OH, xe2x80x94NH2, 
and 
and R5-R8 independently denote a substituent selected from the group consisting of hydrogen, halogen, alkyl, alkoxy and nitro;
Formula (2): 
wherein R9 denotes a substituent selected from the same group as for R4,
Formula (3): 
wherein R10-R12 independently denote a substituent selected from the same group as for R1-R3.
According to the present invention, there is also provided an image forming method, comprising:
(a) a charging step of charging an image-bearing member by means of a charging member supplied with a voltage form an external voltage supply,
(b) a latent image forming step of forming an electrostatic image on the charged image-bearing member,
(c) a developing step of developing the electrostatic image with the above-mentioned toner carried on a developer-carrying member to form a toner image on the image-bearing member,
(d) a transfer step of transferring the toner image on the image-bearing member onto a transfer material via or without via an intermediate transfer member,
(e) a cleaning step of removing transfer residual toner remaining on the image-bearing member, and
(f) a fixing step of fixing the toner image onto the transfer material under application of heat and pressure from heat-pressure means.
In an embodiment of the present invention, in the above transfer step (d), a transfer member is abutted against the image-bearing member or the intermediate transfer member via the transfer material.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.